Handling and manipulating small quantities of liquids are fundamental challenges in modern biology. Microfluidic technologies have offered means to reduce sample and reagent consumption while increasing automation. Critical to realizing these goals are integrated valves, which enable routing, pumping, and isolation of submicroliter volumes of liquid. Most current valves are pneumatically actuated and require pressure tanks, regulators, and off-chip solenoid valves to control on-chip fluid manipulation.
Attempts have been made to eliminate the external control required for pneumatic valves. These include efforts to develop thermally actuated valves using thermally deflecting materials or bimetals and locally patterned thermally expansive materials including wax, plastic, gas, liquid, hydrogels, and composites. Previous efforts have not been widely adopted because they were one-time use valves, involved complex many-step fabrication processes, were greater than millimeter scale, were not rigorously tested, thoroughly characterized, or multiplexed, took greater than 5 seconds to actuate, were not amenable to high throughput manufacturing, or did not completely close.
What is needed is a device that enables complex liquid handling without the expensive, bulky, and high power consumption external equipment required by pneumatic systems.